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United States Patent |
6,017,831
|
Beardsley
,   et al.
|
January 25, 2000
|
Nonwoven abrasive articles
Abstract
Abrasive articles and a method for the manufacture of such articles are
described. The articles comprise a lofty nonwoven web of fibers, the
fibers defining a first major web surface, a second major web surface and
a middle web portion extending between the first and second major web
surfaces; and a plurality of abrasive particles adhered to the surfaces of
the fibers of at least one of the first or second major web surfaces and
distributed along the lengths of the fibers in a substantially uniform
manner, the particles comprising a distribution of particle sizes having a
median particle diameter of about 60 microns or less.
Inventors:
|
Beardsley; Kris A. (Roseville, MN);
Lise; Jonathan M. (Woodbury, MN);
Niccum; Brent D. (North St. Paul, MN)
|
Assignee:
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3M Innovative Properties Company (St. Paul, MN)
|
Appl. No.:
|
952678 |
Filed:
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November 12, 1997 |
PCT Filed:
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May 3, 1996
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PCT NO:
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PCT/US96/06287
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371 Date:
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November 12, 1997
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102(e) Date:
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November 12, 1997
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PCT PUB.NO.:
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WO97/42005 |
PCT PUB. Date:
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November 13, 1997 |
Current U.S. Class: |
442/68; 51/295; 51/297; 51/298; 51/307; 442/69; 442/74; 442/75; 442/148; 442/293 |
Intern'l Class: |
B24D 003/00; B24D 003/28; B24D 003/34; A47L 013/17 |
Field of Search: |
442/68,69,74,75,148,293
51/295,297,298,307
|
References Cited
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Other References
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|
Primary Examiner: Weisberger; Richard
Attorney, Agent or Firm: Pastirik; Daniel R., Bardell; Scott A.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a National Application filed under 35 U.S.C. .sctn.371
from International Application No. PCT/US96/06287, filed on May 3, 1996.
Claims
We claim:
1. An abrasive article, comprising:
a nonwoven web of fibers bonded to one another, the fibers defining a first
major web surface, a second major web surface and a middle web portion
extending between the first and second major web surfaces, the fibers each
having a surface and a length; and
a plurality of abrasive particles adhered to the surfaces of the fibers of
at least one of the first or second major web surfaces and distributed
along the lengths of the fibers in a substantially uniform and continuous
manner and substantially protruding from the fibers of the web, the
particles comprising a distribution of particle sizes having a median
particle of about 60 microns or less.
2. The article as defined in claim 1 wherein the fibers comprise materials
selected from the group consisting of polyester, nylon, polypropylene,
acrylic polymer, rayon, cellulose acetate polymer, polyvinylidene
chloride-vinyl chloride copolymers, vinyl chloride-acrylonitrile
copolymers, cotton, wool, jute, hemp and combinations of the foregoing
materials.
3. The article as defined in claim 1 wherein the fibers are crimped staple
fibers having a fineness within the range of about 1.5 to about 500
denier.
4. The article as defined in claim 1 wherein the fibers are adhesively
bonded to one another at their mutual contact points within the web with a
prebond resin comprising a cured thermosetting adhesive selected from the
group consisting of phenolic resins, aminoplast resins having pendant
.alpha.,.beta.-unsaturated carbonyl groups, urethane resins, epoxy resins,
ethylenically unsaturated resins, acrylated isocyanurate resins,
urea-formaldehyde resins, isocyanurate resins, acrylated urethane resins,
acrylated epoxy resins, bismaleimide resins, fluorene-modified epoxy
resins, and combinations thereof.
5. The article as defined in claim 1 wherein the fibers of the web comprise
melt bondable bicomponent fibers wherein the fibers are bonded to one
another at their mutual contact points by a melted component of the
fibers.
6. The article as defined in claim 1 wherein the abrasive particles are
adhered to the fibers of the nonwoven web by a cured thermosetting
adhesive selected from the group consisting of phenolic resins, aminoplast
resins having pendant .alpha.,.beta.-unsaturated carbonyl groups, urethane
resins, epoxy resins, ethylenically unsaturated resins, acrylated
isocyanurate resins, urea-formaldehyde resins, isocyanurate resins,
acrylated urethane resins, acrylated epoxy resins, bismaleimide resins,
fluorene-modified epoxy resins, and combinations thereof.
7. The article as defined in claim 6 wherein the cured thermosetting
adhesive provides a substantially uniform resin layer over the fibers of
the web.
8. The article as defined in claim 7 wherein the substantially uniform
resin layer comprises separate make and size coatings.
9. The article as defined in claim 1 wherein the abrasive particles
comprise material selected from the group consisting of aluminum oxide,
silicon carbide, alumina zirconia, diamond, ceria, cubic boron nitride,
garnet, and combinations thereof.
10. The article as defined in claim 9 wherein the aluminum oxide is
selected from the group consisting of ceramic aluminum oxide, heat-treated
aluminum oxide, white-fused aluminum oxide and combinations thereof.
11. The article as defined in claim 1 wherein the abrasive particles have a
median diameter ranging from about 0.1 micron to about 60 microns.
12. The abrasive article as defined in claim 1 wherein the abrasive
particles comprise materials selected from thermosetting polymer
particles, thermoplastic polymer particles and combinations of the
foregoing materials.
13. An abrasive article, comprising:
a lofty nonwoven web of fibers bonded to one another, the fibers defining a
first major web surface, a second major web surface and a middle web
portion extending between the first and second major web surfaces, the
fibers each having a surface and a length; and
a plurality of abrasive particles adhered by a cured thermosetting adhesive
to the surfaces of the fibers of at least one of the first or second major
web surfaces, the particles distributed along the lengths of the fibers in
a substantially uniform and continuous manner and substantially protruding
from the fibers of the web and the particles comprising a distribution of
particle sizes having a median particle diameter of about 60 microns or
less.
14. The article as defined in claim 13 wherein the fibers comprise
materials selected from the group consisting of polyester, nylon,
polypropylene, acrylic polymer, rayon, cellulose acetate polymer,
polyvinylidene chloride-vinyl chloride copolymers, vinyl
chloride-acrylonitrile copolymers, cotton, wool, jute, hemp and
combinations of the foregoing materials.
15. The article as defined in claim 13 wherein the fibers are crimped
staple fibers having a linear density within the range of about 1.5 to
about 500 denier.
16. The article as defined in claim 13 wherein the fibers are adhesively
bonded to one another at their mutual contact points within the web with a
prebond resin comprising a cured thermosetting adhesive selected from the
group consisting of phenolic resins, aminoplast resins having pendant
.alpha.,.beta.-unsaturated carbonyl groups, urethane resins, epoxy resins,
ethylenically unsaturated resins, acrylated isocyanurate resins,
urea-formaldehyde resins, isocyanurate resins, acrylated urethane resins,
acrylated epoxy resins, bismaleimide resins, fluorene-modified epoxy
resins, and combinations thereof.
17. The article as defined in claim 13 wherein the fibers of the web
comprise melt bondable bicomponent fibers wherein the fibers are bonded to
one another at their mutual contact points by a melted component of said
fibers.
18. The article as defined in claim 13 wherein the abrasive particles are
adhered to the fibers of the nonwoven web by a cured thermosetting
adhesive selected from the group consisting of phenolic resins, aminoplast
resins having pendant .alpha.,.beta.-unsaturated carbonyl groups, urethane
resins, epoxy resins, ethylenically unsaturated resins, acrylated
isocyanurate resins, urea-formaldehyde resins, isocyanurate resins,
acrylated urethane resins, acrylated epoxy resins, bismaleimide resins,
fluorene-modified epoxy resins, and combinations thereof.
19. The article as defined in claim 18 wherein the cured thermosetting
adhesive provides a substantially uniform resin layer over the fibers of
the web.
20. The article as defined in claim 13 wherein the abrasive particles
comprise material selected from the group consisting of aluminum oxide,
silicon carbide, alumina zirconia, diamond, ceria, cubic boron nitride,
garnet, and combinations thereof.
21. The article as defined in claim 20 wherein the aluminum oxide is
selected from the group consisting of ceramic aluminum oxide, heat-treated
aluminum oxide, white-fused aluminum oxide and combinations thereof.
22. The article as defined in claim 13 wherein the abrasive particles have
a median diameter ranging from about 0.1 micron to about 60 microns.
Description
The present invention relates to abrasive articles having a desired
distribution of fine abrasive particles.
BACKGROUND OF THE INVENTION
Nonwoven webs comprising open, lefty, three dimensional structures of
fibers bonded to one another at their mutual contact points are used
extensively in the manufacture of abrasive articles for cleaning,
abrading, finishing and polishing applications on any of a variety of
surfaces. Exemplary of such nonwoven articles are those described in U.S.
Pat. No. 2,958,593 to Hoover et al. Such nonwoven webs comprise a suitable
fiber such as nylon, polyester, blends thereof and the like and are
capable of withstanding temperatures at which impregnating resins and
adhesive binders are typically cured. The fibers of the web are often
tensilized and crimped but may also be continuous filaments formed by an
extrusion process such as that described in U.S. Pat. No. 4,227,350 to
Fitzer, for example. Nonwoven webs are readily formed on conventional
equipment such as a "Rando Webber" machine (commercially available from
Rando Machine Company, New York), for example.
Fine abrasive particles (defined herein as particles having a distribution
of sizes wherein the median particle diameter in the distribution is about
60 microns or less) may be bonded to the fibers of a nonwoven web to
provide abrasive articles suitable for use in any of a variety of abrasive
applications, and such articles may be provided in the form of endless
belts, discs, hand pads, densified or compressed wheels, floor polishing
pads and the like. A particularly appropriate use for articles comprising
the aforementioned fine particles is in the automotive aftermarket
industry, where the abrasive particles are employed to "scuff" or lightly
abrade automobile body panels in preparation for painting. In these
applications, the abrasive article is applied to a previously painted
surface. During the application, the abrasive particles in the article
scratch the surface to reduce the surface gloss to a "haze". Although the
commercial success of available abrasive articles has been impressive, it
is desirable to further improve the performance of certain abrasive
articles especially in applications in the automotive aftermarket, for
example.
In the manufacture of these articles, a nonwoven web is prepared, as
mentioned. The web is reinforced, for example, by the application of a
prebond resin to bond the fibers at their mutual contact points.
Additional resin layers may subsequently be applied to the prebonded web.
A make coat precursor is applied over the fibers of the prebonded web and
the make coat precursor is at least partially cured. A size coat precursor
may be applied over the make coat precursor and both the make coat
precursor and the size coat precursor are sufficiently hardened in a known
manner (e.g., by heat curing). Fine abrasive particles, when included in
the construction of the article, are conventionally applied to the fibers
in a slurry with the make coat precursor.
Prior to or during the curing of the make coat, the resinous slurry of make
coat precursor and fine abrasive particles is known to migrate and to
concentrate or agglomerate at the intersection of two or more fibers in
the web, or at points where a single fiber crosses itself due to known
surface tension effects, for example. The resulting abrasive articles have
a substantially nonuniform distribution of the agglomerated resin and the
fine abrasive particles along the lengths of the fibers. Further, because
the particles are applied to the web in a resinous slurry, the fine
abrasive particles tend to become engulfed in the cured resin, as is
illustrated in FIG. 1 wherein the resinous adhesive forms agglomerates 12
along the lengths of the fibers 10 of the nonwoven web with the fine
abrasive particles dispersed and engulfed within the resin. In such a
construction, the fine abrasive particles may not be immediately available
in abrading applications of the finished article, possibly making the
overall abrasive performance of the articles less than optimum and leaving
room for improvement in performance. In the automotive aftermarket
industry, for example, the initial unavailability of the abrasive
particles can result in an undesirably low initial abrasive action when
the article is applied to the surface, prompting the user to exert high
pressures on the article during the abrasive operation which may have an
undesired effect on the surface being treated.
Historically, lofty, open, 3-dimensional nonwoven abrasive articles have
been made using a variety of coating techniques. In the aforementioned
U.S. Pat. No. 2,958,593 (Hoover et al.) for example, nonwoven articles
were made by the spray application of a relatively dilute slurry
comprising a solution of binder, organic solvent and abrasive particles.
It was expected that other coating methods and procedures might provide
advantages under specific circumstances.
From Hoover et al.:
It should be noted, however, that by employing techniques other than
spraying, somewhat greater thicknesses of web may be suitably treated in
forming our structures. In fact, roll coating, dip coating, separate
application of adhesive and mineral, etc., may have advantages over the
spray application described in the previous examples. For instance,
spraying the adhesive first and then sifting in the abrasive separately is
particularly suitable for incorporating coarse mineral, (e.g. grit 50 or
larger), and also results in products of slightly differing abrading
characteristics.
With the passage of time, it became desirable to minimize resin waste from
overspray and minimize or eliminate volatile organic compounds from use in
the manufacturing process. Consequently, the spray coating techniques
exemplified by Hoover et al. generally fell into disfavor, and the present
day use of roll coating techniques to apply water-based resin/abrasive
slurries began in earnest. As the performance characteristics of nonwoven
abrasive articles became more demanding, the resin/abrasive coatings
employed in the manufacture of nonwoven abrasive articles and methods for
the application of such coatings have continued to evolve. However, the
foregoing problem of uniformly coating fine abrasive particles onto the
fibers of a nonwoven web has persisted.
Efforts to overcome the problem of resin and particle agglomeration in the
application of fine abrasive particles to nonwovens include attempted drop
coating or spray coating techniques, as taught or suggested by Hoover et
al. In these efforts, dry abrasive particles are deposited onto the fibers
of the web after the application of the uncured make coat precursor.
However, in the deposition of fine abrasive particles by these techniques,
the distribution of the particles is greatly influenced by electrostatic
forces and ambient moisture conditions which occur naturally in the
materials (e.g., the particles) and in the equipment used in the
deposition process. As a result of these forces, fine abrasive particles
have shown a consistent tendency to agglomerate while still resident
within the coating equipment as well as after the particles have been
released therefrom. This particle to particle interaction or agglomeration
may result in abrasive articles comprising significant particle
agglomerates with non-uniform particle distributions within the resulting
webs. Such articles may possess nonuniform performance characteristics,
and the nonuniformity of the particle distribution, with the presence of
particle agglomerates, can create a commercially unacceptable appearance
in the article. Moreover, standard roll coating techniques used in the
application of the make coat precursor can add excessive amounts of the
resin to the web, resulting in resin layers which can readily engulf fine
abrasive particles once they are applied to the web.
Accordingly, it is desirable to solve the above described problem and to
thereby fulfill a long felt need relating to the optimization of fine
abrasive particle distribution in nonwoven abrasive articles. It is
desirable to provide nonwoven abrasive articles comprising a nonwoven web
with fine abrasive particles adhered to the fibers of the web wherein the
particles are distributed along the lengths of the fibers of the web in a
substantially uniform manner and wherein an increased percentage of the
abrasive particles are immediately available for abrasive applications of
the finished article.
SUMMARY OF THE INVENTION
The present invention provides nonwoven abrasive articles which include
fine abrasive particles adhered to the fibers of a nonwoven web in a
desirable particle distribution. The articles are useful in abrasive
applications such as finishing and polishing of metal, wood and plastic
surfaces, for example, and especially in the automobile aftermarket
industry where the articles are useful to treat painted automobile panels
and the like. In the manufacture of such articles, fine abrasive particles
are deposited onto the fibers of the nonwoven web so that the particles
are distributed in a substantially uniform manner along the surfaces of
the fibers to provide an abrasively effective article.
In describing the present invention, "prebond resin" refers to a coatable
resinous adhesive applied directly to the fibers of an unbonded nonwoven
web in order to bond the fibers together at their mutual contact points.
"Prebonded web" refers to a nonwoven web wherein the fibers of the web
have been treated with a prebond resin and the resin has been hardened to
bond the fibers at their mutual contact points. "Make coat precursor"
refers to the coatable resinous adhesive material applied to the fibers of
the nonwoven web to secure abrasive particles thereto. "Make coat" refers
to the layer of hardened resin over the fibers of the nonwoven web formed
by hardening the make coat precursor. "Size coat precursor" refers to the
coatable resinous adhesive material applied to the fibers of the nonwoven
web over the make coat. "Size coat" refers to the layer of hardened resin
over the fibers of the nonwoven web formed by hardening the size coat
precursor. "Cured" or "fully cured" means a hardened polymerized curable
coatable resin. "Fiber" refers to a threadlike structure. "Fine abrasive
particles" refers to abrasively effective particles comprising any of the
materials set forth herein and having distribution of particle sizes
wherein the median particle diameter is about 60 microns or less. A
spherical particle shape is assumed in referring to the median particle
diameter, based on standard test methods available for the determination
of particle diameters such as, for example ANSI test method B74.18-1884.
"Substantially uniform" in referring to the distribution of fine abrasive
particles along the length of the fibers means that the particles in the
finished articles are distributed along the lengths of the fibers without
significant agglomeration of the resin and the particles, as may be
visually observed by microscopic examination of the fibers. In the
finished article, the majority of the particles are positioned along the
fibers to be abrasively effective in the initial application of the
article.
In referring to the binder compositions of the make and size coats,
"Labile" means a foamed condition imparted to a liquid dispersion of
binder material (e.g., a make coat precursor or a size coat precursor) so
that the foamed state of the binder dispersion is transitory. By the term
"foam", it is meant a dispersion of gas bubbles throughout a liquid where
each bubble is enclosed within a thin film of the liquid. The labile foams
utilized in the invention thus also encompass "froths" or unstable foam
consisting of relatively large bubbles of gas.
In one aspect, the invention provides an abrasive article, comprising:
a nonwoven web of fibers bonded to one another, the fibers defining a first
major web surface, a second major web surface and a middle web portion
extending between the first and second major web surfaces, the fibers each
having a surface and a length; and
a plurality of abrasive particles adhered to the surfaces of the fibers of
at least one of the first or second major web surfaces and distributed
along the lengths of the fibers in a substantially uniform manner, the
particles comprising a distribution of particle sizes having a median
particle diameter of about 60 microns or less.
The fibers of the nonwoven web may be bonded to one another at their points
of mutual contact by utilizing a prebonded web or a web comprising melt
bondable fibers bonded to one another at their mutual contact points by a
melted component of the fibers. The web may also be consolidated by needle
tacking, for example. Additionally, the fibers of the nonwoven web may be
bonded to one another at first and second bonding sites with a nonbonded
portion of the filament array in between the first and second bonding
sites. Fine abrasive particles are preferably dispersed throughout the
web. However, it is also contemplated that only the fibers of the first
and/or second major web surfaces will include fine abrasive particles
adhered thereto, and the particles may comprise any of a variety of
suitable abrasive materials. The particles are bonded to the fibers of the
nonwoven web with a suitable adhesive which may comprise thermoplastic or
thermosetting resins. Preferably, the particles are secured to the fibers
utilizing a thermosetting phenolic resin make coat and, optionally, a
similar size coat. The articles of the invention may be provided in the
form of hand pads, endless belts, discs, densified or compressed wheels
and the like. Additionally, the articles of the invention can be laminated
to other articles such as sponges and the like or the articles can be
provided a in a roll form with or without perforations therein.
In the preparation of the foregoing articles, a lofty nonwoven web of
fibers is prepared or is otherwise provided. A make coat precursor
composition is applied to the external surface of the fibers to form a
first coating layer. A plurality of the foregoing fine abrasive particles
is applied to the first coating layer, and the make coat precursor
composition is at least partially cured. Optionally, a size coat precursor
composition is applied over the abrasive particles and the first coating
layer to form a second coating layer. The first and second coating layers
are cured to affix the abrasive particles to the fibers of the nonwoven
web to provide the abrasive article wherein the particles are affixed to
the fibers in a substantially uniform distribution along the lengths
thereof.
The fine abrasive particles are deposited onto the make coat precursor,
preferably by depositing the particles first on one major surface of the
web and then over the second major surface of the web using the deposition
method described in commonly assigned co-pending U.S. patent application
Ser. No. 08/930,098, entitled "Method Of Manufacturing Nonwoven Articles",
filed concurrently herewith, now U.S. Pat. No. 5,863,305. Preferably, the
make and size coat precursors are thermosetting, coatable, phenolic resins
which are provided as labile foams. The make coat precursor is frothed
prior to its application to the web, and is thereafter allowed to at least
partially break down prior to the application of abrasive particles.
Likewise, the optional size coat, when applied to the article, is
preferably frothed and then applied over the at least partially cured make
coat. The make coat precursor and size coat precursor are then fully cured
to provide the abrasive articles of the invention, and the thus prepared
articles may be further processed to provide hand pads, endless belts,
discs, densified or compressed wheels and the like.
The additional details of the invention will be more fully appreciated by
those skilled in the art upon consideration of the remainder of the
disclosure including the detailed description of the preferred embodiment
and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
In describing the various aspects of the preferred embodiment, reference is
made to the Figures, wherein:
FIG. 1 is an enlarged view of a portion of a prior art abrasive article
showing individual fibers of a nonwoven web;
FIG. 2 is an enlarged view of a portion of a abrasive article showing
individual fibers with abrasive particles adhered to the surface of the
fibers according to the invention;
FIG. 3 is a partially schematic view of a method and apparatus for
manufacturing lofty nonwoven abrasive articles according to the present
invention;
FIG. 4 is a partially schematic view of one embodiment of a particle coater
according to the present invention;
FIG. 5 is an elevational view of an alternate particle sprayer for use with
the present invention;
FIG. 6 is a partial cross-sectional view of the nozzle of FIG. 5 taken
along line 6--6;
FIG. 6A is a view like FIG. 6 of an alternate embodiment of the nozzle;
FIG. 7 is a cross-sectional view of a further alternate embodiment of a
particle sprayer for use with the present invention; and
FIGS. 8A through 8D are schematic plan views of alternate patterns of the
coating apparatus of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Details of the preferred embodiment of the invention will now be described.
It will be understood by those skilled in the art that the details of the
embodiments discussed below are not intended to be limiting in any way but
merely illustrative of the features of the invention. In describing the
preferred embodiment, reference is made to the figures wherein structural
features are identified by reference numerals and wherein identical
reference numerals indicate identical structures.
As shown in FIG. 2, the articles of the invention comprise an open, lofty,
nonwoven web of fibers 100 which preferably have been bonded to one
another at their mutual contact points by a cured prebond resin.
Alteratively, the web can comprise melt bondable biocomponent fibers
wherein the fibers are of a sheath-core or side by side configuration and
which have been heated to the melting point of at least one component of
the fibers to cause melt bonding between the fibers at their contact
points. Suitable melt bondable fibers include those described by Hayes et
al. in U.S. Pat. No. 5,082,720, the disclosure of which is incorporated
herein by reference. A plurality of fine abrasive particles 102 are bonded
to the fibers 100 by cured resinous binders applied to the web to provide
make and size coats, as described herein. The abrasive particles 102 are
arranged in a preferred distributor along the fibers 100 so that the
particles 102 are distributed in a substantially uniform manner along the
fibers and without burying the fibers in agglomerated resin. In this
construction, the particles 102 are positioned to be immediately effective
in initial abrasive applications of the finished article, such as in the
treatment of painted automobile body panels, for example.
The nonwoven web suitable for use in the articles of the invention may be
made of an air-laid, carded, stitch-bonded, spunbonded, wet laid, or melt
blown construction. A preferred nonwoven web is the open, loft,
three-dimensional air-laid nonwoven substrate described by Hoover et al.
in U.S. Pat. No. 2,958,593, incorporated herein by reference.
Alternatively, the nonwoven web used herein can be a low density nonwoven
article formed of a multiplicity of crimped filaments (e.g., thermoplastic
filaments) wherein one end of substantially all of the filaments are
bonded together at a first bonding site and a second end of substantially
all of the filaments are bonded together at a second bonding site with a
nonbonded portion of the filament array in between the first and second
bonding sites. Such a nonwoven web is described in U.S. Pat. Nos.
4,991,362 and 5,025,596, both to Heyer et al. the disclosures of which are
incorporated herein by reference.
The nonwoven web preferably comprises a first major web surface, a second
major web surface, and a middle web portion extending between the first
and second major web surfaces. The web is made of a suitable synthetic
fiber capable of withstanding the temperatures at which impregnating
resins and adhesive binders are cured without deterioration. Fibers
suitable for use in the articles of the invention include natural and
synthetic fibers, and mixtures thereof. Synthetic fibers are preferred
including those made of polyester (e.g., polyethylene terephthalate),
nylon (e.g., hexamethylene adipamide, polycaprolactum), polypropylene,
acrylic (formed from a polymer of acrylonitrile), rayon, cellulose
acetate, polyvinylidene chloride-vinyl chloride copolymers, vinyl
chloride-acrylonitrile copolymers, and so forth. Suitable natural fibers
include those of cotton, wool, jute, and hemp. The fiber used may be
virgin fibers or waste fibers reclaimed from garment cuttings, carpet
manufacturing, fiber manufacturing, or textile processing, for example.
The fiber material can be a homogenous fiber or a composite fiber, such as
bicomponent fiber (e.g., a co-spun sheath-core fiber). It is also within
the scope of the invention to provide an article comprising different
fibers in different portions of the web (e.g., the first web portion, the
second web portion and the middle web portion). The fibers of the web are
preferably tensilized and crimped but may also be continuous filaments
formed by an extrusion process such as that described in U.S. Pat. No.
4,227,350 to Fitzer, incorporated herein by reference, as well as the
continuous fibers described by the aforementioned '362 and '596 patents to
Heyer et al.
Where the nonwoven web is of the type described by Hoover et al.,
identified above, satisfactory fibers for use in the nonwoven web are
between about 20 and about 110 millimeters and preferably between about 40
and about 65 millimeters in length and have a fineness or linear density
ranging from about 1.5 to about 500 denier and preferably from about 15 to
about 110 denier. It is contemplated that fibers of mixed denier can be
used in the manufacture of a nonwoven web in order to obtain a desired
surface finish. The use of larger fibers is also contemplated, and those
skilled in the art will understand that the invention is not limited by
the nature of the fibers employed or by their respective lengths, linear
densities and the like.
The aforementioned nonwoven web is readily formed on a "Rando Webber"
machine (commercially available from Rando Machine Company, New York) or
may be formed by other conventional processes. Where a spunbonded-type
nonwoven material is employed, the filaments may be of substantially
larger diameter, for example, up to 2 millimeters or more in diameter.
Useful nonwoven webs preferably have a weight per unit area at least about
50 g/m.sup.2, preferably between 50 and 200 g/m.sup.2, more preferably
between 75 and 150 g/m.sup.2. Lesser amounts of fiber within the nonwoven
web will provide articles which may be suitable in some applications, but
articles with lower fiber weights may have somewhat shorter commercial
work lives. The foregoing fiber weights typically will provide a web,
before needling or impregnation, having a thickness from about 5 to about
200 millimeters, typically between 6 to 75 millimeters, and preferably
between 10 and 30 millimeters.
The nonwoven web may optionally be reinforced and consolidated by needle
tacking, a treatment which mechanically strengthens the nonwoven web by
passing barbed needles therethrough. During this treatment, the needles
pull the fibers of the web with them while they pass through the nonwoven
web so that, after the needle has retracted, individual collections of
fibers of the web are oriented in the thickness direction of the nonwoven
fabric. The amount or degree of needle tacking may include the use of
about 8 to about 20 needle penetrations per square centimeter of web
surface when 15.times.18.times.25.times.3.5 RB, F20 6-32-5.5B/3B/2E/L90
needles (commercially available from Foster Needle Company, Manitowoc,
Wis.) are used. Needle tacking is readily accomplished by use of a
conventional needle loom which is commercially available from, for
example, Dilo, Inc. of Charlotte, N.C.
Where the web is to be incorporated into machine driven abrasive articles
such as endless belts or abrasive discs, a reinforcing fabric backing may
be applied and affixed to one of the major surfaces of the web. The
reinforcing fabric is preferably a woven stretch-resistant fabric with a
low-stretch value when pulled in opposing directions. A stretch value of
less than about 20% is preferred and a value of less than about 15% is
more preferred. Suitable materials for use as the reinforcing fabric in
the articles of the invention include, without limitation, thermobonded
fabrics, knitted fabrics, stitch-bonded fabrics and the like. Those
skilled in the art will appreciate that the invention is not to be limited
to the selection of one reinforcing fabric over another, and it is
contemplated that the invention can include any type of material which
otherwise has the requisite properties as set forth herein. The fabric
backing may be adhesively affixed to the nonwoven web or it may be affixed
during the aforementioned needletacking step, all in a known manner. An
additional layer comprising a suitable polymer may then be applied over
the exposed surface of the fabric backing in the manner described in
commonly assigned U.S. Pat. No. 5,482,756, issued Jan. 9, 1996 and
incorporated herein by reference, or in the manner described in commonly
assigned U.S. patent application Ser. No. 08/369,933 filed Jan. 6, 1995,
now U.S. Pat. No. 5,573,844, incorporated herein by reference.
The prebond resin, when used to bond fibers in the web to one another at
their mutual contact points, preferably comprises a coatable resinous
adhesive similar or identical to the resin used for the make coat
precursor, described below. More preferably, the prebond is made of a
thermosetting water based phenolic resin. The prebond is applied to the
web in a relatively light coating, typically providing a dry add-on weight
within the broad range from about 50 to 200 g/m.sup.2 for phenolic prebond
resins applied to a nonwoven web having a fiber weight within the above
ranges. Polyurethane resins may also be employed as well as other resins,
and those skilled in the art will appreciate that the selection and amount
of resin actually applied can depend on any of a variety of factors
including, for example, the fiber weight in the nonwoven web, the fiber
density, the fiber type as well as the contemplated end use for the
finished article. Of course, the present invention does not require the
use of a prebond resin and the invention is not to be constructed as being
limited to nonwoven webs comprising any particular prebond resin.
As is described in more detail below, an adhesive layer is formed from the
application to the web of a resinous make coat precursor or first resin
and, optionally, a size coat precursor or second resin applied over the
make coat precursor. Preferably, the adhesive layer is formed from the
make coat precursor and the size coat precursor which have been applied to
the web at a coating weight which, when hardened, provides the necessary
adhesion to strongly bond abrasive particles to the fibers. In the
finished articles of the invention, the adhesive layer provide sa light
coating of resin over the fine abrasive particles without burying the
particles within the resin. When observed under a microscope, for example,
the individual particles are observed to be anchored to the fibers and to
extend outwardly from the outer surfaces of the fibers. In this
construction, the fine abrasive particles are positioned in the article to
be immediately abrasively effective in the initial applications of the
finished article. Moreover, the particles are strongly adhered to the
fibers of the web to provide an abrasive article with a satisfactory work
life.
The make coat precursor suitable for use in the invention is a coatable,
hardenable adhesive binder and may comprise one or more thermoplastic or,
preferably, thermosetting resinous adhesives. Resinous adhesives suitable
for use in the present invention include phenolic resins, aminoplast
resins having pendant .alpha.,.beta.-unsaturated carbonyl groups, urethane
resins, epoxy resins, ethylenically unsaturated resin, acrylated
isocyanurate resins, urea-formaldehyde resins, isocyanurate resins,
acrylated urethane resins, acrylated epoxy resins, bismaleimide resins,
fluorene-modified epoxy resins, and combinations thereof. Catalysts and/or
curing agents may be added to the binder precursor to initiate and/or
accelerate the polymerization process.
Epoxy resins have an oxirane and are polymerized by the ring opening. Such
epoxide resins include monomeric epoxy resins and polymeric epoxy reins.
These resin can vary greatly in the nature of their backbones and
substituent groups. For example, the backbone may be of any type normally
associated with epoxy resins and substituent groups thereon can be any
group free of an active hydrogen atom that is reactive with an oxirane
ring at room temperature. Representative examples of acceptable
substituent groups include halogens, ester groups, ether groups, sulfonate
groups, siloxane groups, nitro groups and phosphate groups. Examples of
some preferred epoxy resins include
2,2-bis[4-(2,3-epoxypropoxy)-phenyl)propane (diglycidyl either of
bisphenol a)] and commercially available materials under the trade
designation "Epon 828", "Epon 1004" and "Epon 1001F" available from Shell
Chemical Co., "DER-331", "DER-332" and "DER-334" available from Dow
Chemical Co. Other suitable epoxy resins include glycidyl ethers of phenol
formaldehyde novolac (e.g., "DEN-431" and "DEN-428" available from Dow
Chemical Co.
Examples of ethylenically unsaturated binder precursors include aminoplast
monomer or oligomer having pendant alpha, beta unsaturated carbonyl
groups, ethylenically unsaturated monomers or oligomers, acrylated
isocyanurate monomers, acrylated urethane oligomers, acrylated epoxy
monomers or oligomers, ethylenically unsaturated monomers or diluents,
acrylate dispersions or mixtures thereof.
The aminoplast binder precursors have at least one pendant alpha,
beta-unsaturated carbonyl group per molecule or oligomer. These materials
are further described in U.S. Pat. Nos. 4,903,440 (Larson et al.) and
5,236,472 (Kirk et al.), both incorporated herein by reference.
The ethylenically unsaturated monomers or oligomers may be monofunctional,
difunctional, trifunctional or even higher functionality. The term
acrylate includes both acrylates and methacrylates. Ethylenically
unsaturated binder precursors include both monomeric and polymeric
compounds that contain atoms of carbon, hydrogen and oxygen, and
optionally, nitrogen and the halogens. Oxygen or nitrogen atoms or both
are generally present in ether, ester, urethane, amide, and urea groups.
Ethylenically unsaturated compounds preferably have a molecule weight of
less than about 4,000 and are preferably esters made from the reaction of
compounds containing aliphatic monohydroxy groups or aliphatic polyhydroxy
groups and unsaturated carboxylic acids, such as acrylic acid, methacrylic
acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, and the
like. Representative examples of ethylenically unsaturated monomers
include methyl methacrylate, ethyl methacrylate, styrene, divinylbenzene,
hydroxy ethyl acrylate, hydroxy ethyl methacrylate, hydroxy propyl
acrylate, hydroxy propyl methacrylate, hydroxy butyl acrylate, hydroxy
butyl methacrylate, vinyl toluene, ethylene glycol diacrylate,
polyethylene glycol diacrylate, ethylene glycol dimethacrylate, hexanediol
diacrylate, triethylene glycol diacrylate, trimethylolpropane triacrylate,
glycerol triacrylate, pentaerthyitol triacrylate, pentaerythritol
trimethacrylate, pentaerythritol tetraacrylate and pentaerythritol
tetramethacrylate. Other ethylenically unsaturated resins include
monoallyl, polyallyl, and polymethallyl esters and amides of carboxylic
acids, such as diallyl phthalate, diallyl adipate, and
N,N-diallyladipamide. Still other nitrogen containing compounds include
tris(2-acryl-oxyethyl)isocyanurate,
1,3,5-tri(2-methyacryloxyethyl)-s-triazine, acrylamide, methylacrylamide,
N-methyl-acrylamide, N,N-dimethylacrylamide, N-vinyl-pyrrolidone, and
N-vinyl-piperidone.
Isocyanurate derivatives having at least one pendant acrylate group and
isocyanurate derivatives having at least one pendant acrylate group are
further described in U.S. Pat. No. 4,652,274 (Boettcher et al.),
incorporated herein by reference. The preferred isocyanurate material is a
triacrylate of tris(hydroxy ethyl)isocyanurate.
Acrylated urethanes are diacrylate esters of hydroxy terminated isocyanate
extended polyesters or polyethers. Examples of commercially available
acrylated urethanes include "UVITHANE 782", available from Morton
Chemical, and "CMD 6600", "CMD 8400", and "CMD 8805", available from UCB
Radcure Specialties. Acrylated epoxies are diacrylate esters of epoxy
resins, such as the diacrylate esters of bisphenol A epoxy resin. Examples
of commercially available acrylated epoxies include "CMD 3500", "CMD
3600", and "CMD 3700", available from UCB Radcure Specialties.
Acrylated urethanes are diacrylate esters of hydroxy terminated NCO
extended polyesters or polyethers. Examples commercially available
acrylated urethanes include UVITHANE 782, available from Morton Thiokol
Chemical, and CMD 6600, CMD 8400, and CMD 8805, available from Radcure
Specialties.
Acrylated epoxies are diacrylate esters of epoxy resins, such as the
diacrylate esters of bisphenol A epoxy resin. Examples of commercially
available acrylated epoxies include CMD 3500, CMD 3600, and CMD 3700,
available from Radcure Specialties.
Examples of ethylenically unsaturated diluents or monomers can be found in
U.S. patent application Ser. No. 08/5,236,472 (Kirk et al.) and U.S.
patent application Ser. No. 08/144,199 (Larsen et al.); the disclosures of
both patent applications are incorporated herein by reference. In some
instances these ethylenically unsaturated diluents are useful because they
tend to be compatible with water.
Additional details concerning acrylate dispersions can be found in U.S.
Pat. No. 5,378,252 (Follensbee), incorporated herein by reference.
It is also within the scope of this invention to use a partially
polymerized ethylenically unsaturated monomer in the binder precursor. For
example, an acrylate monomer can be partially polymerized and incorporated
into the make coat precursor. The degree of partial polymerization should
be controlled so that the resulting partially polymerized ethylenically
unsaturated monomer does not have an excessively high viscosity so that
the binder precursor is a coatable material. An example of an acrylate
monomer that can be partially polymerized is isooctyl acrylate. It is also
within the scope of this invention to use a combination of a partially
polymerized ethylenically unsaturated monomer with another ethylenically
unsaturated monomer and/or a condensation curable binder.
In the manufacture of hand pads for use in the automotive applications
mentioned above, the adhesive materials used as the make coat precursor in
the present invention preferably comprise thermosetting phenolic resins
such as resole and novolac resins, described in Kirk-Othmer, Encyclopedia
of Chemical Technology, 3d Ed. John Wiley & Sons, 1981, New York, Vol. 17,
pp. 384-399, incorporated herein by reference. Resole phenolic resins are
made with an alkaline catalyst and a molar excess of formaldehyde,
typically having a molar ratio of formaldehyde to phenol between 1.0:1.0
and 3.0:1.0. Novolac resins are prepared under acid catalysis and with a
molar ratio of formaldehyde to phenol less than 1.0:1.0. A typical resole
resin useful in the manufacture of articles of the present invention
contains between about 0.75% (by weight) and about 1.4% free formaldehyde;
between about 6% and about 8% free phenol; about 78% solids with the
remainder being water. The pH of such a resin is about 8.5 and the
viscosity is between about 2400 and about 2800 centipoise. Commercially
available phenolic resins suitable for use in the present invention
include those known under the trade designations "Durez" and "Varcum",
available from Occidental Chemicals Corporation (N. Tonawonda, N.Y.);
"Resinox", available from Monsanto Corporation; and "Arofene" and
"Arotap", both available from Ashland Chemical Company; as well as the
resole precondensate available under the trade designation "BB077" from
Neste Resins, a Division of Neste Canada, Inc., Mississauga, Ontario,
Canada. Organic solvent may be added to the phenolic resin as needed or
desired.
Preferably, the adhesive binder used as the make coat is foamed or frothed
prior to its application to the fibers of the nonwoven web. The binder
composition can be an aqueous dispersion of a binder that hardens upon
drying. Most preferred among these binder compositions are foamable,
coatable, hardenable resole phenolic resins comprising a surface active
agent to assist in the formation of the foam and to enhance its stability.
An exemplary commercially available surface active agent is that known
under the trade designation "SULFOCHEM SLS" from Chemron Corporation of
Paso Robles, Calif. Such foaming agents (emulsifiers) or surfactants are
added to the make coat resin and are applied to the nonwoven web using
coating methods compatible with liquid coatings. Amounts nearing 1.0% to
6.0%, and preferably about 3% of the total wet components have been used.
The foamable, coatable, hardenable resin composition useful as a make coat
precursor in the present invention should be able to retain its foam form
for a sufficient length of time to allow the application of the foam to
the non-woven web before the foam breaks significantly. Preferably, the
foamed make coat will begin to break soon after its application to the
nonwoven web so that the application of the abrasive particles can be
accomplished in a manner which allows the particles to penetrate into the
web beyond the uppermost surface layers of fibers. The resin compositions
may be foamed by known methods, such as by mechanically foaming or
frothing, by the injection and dispersion of insoluble gas, or by the use
of chemical blowing agents that thermally or otherwise decompose to
produce a gas-phase material. For the purposes of the present invention,
the foamable, coatable, hardenable resin compositions should be foamable
to a blow ratio, i.e., the ratio of foamed volume to that of the unfoamed
starting material, of between 2:1 and 99:1. Phenolic foamed binder resin
dispersions preferably will have a gas content of at least 20% by volume
and more preferably between 50% and 99% (or a blow ratio of between 2:1
and 99:1, preferably between 5:1 and 25:1 and more preferably about 10:1).
The labile foam must retain its structural integrity at least until the
foam is applied to the fibers of the web in order to reduce the wet add-on
weight of the resin being applied to the fiber layer. Foaming of the make
coat provides a desired and economically attractive reduction in the
add-on weight of the resin because the foamed resin is highly diluted with
air, significantly increasing the volume of the resin while utilizing a
smaller amount than would be required in the absence of foaming. The
application of the foamed resin to the fibers of the web creates a
substantially uniform monolayer of resin along the lengths of the fibers
which, in turn, provides the bonding surface for the fine abrasive
particles.
The foamed resin is applied to the nonwoven web to provide an amount when
dried to provide a sheath-like covering over the fibers of the nonwoven
web. For webs having the aforementioned fiber weights, the frothed
phenolic make coat precursor add-on weight is preferably within the range
from about 33 g/m.sup.2 to about 105 g/m.sup.2. The specific add-on
weights to be used will depend on several factors such as the nature of
the nonwoven web (e.g., fiber weights, fiber types and the like) as well
as the nature of the resin being used. The determination of appropriate
make coat add-on weights is well within the skill of those practicing in
the field.
The abrasive particles suitable for inclusion in the abrasive articles of
the present invention include all known fine abrasive particles.
Preferably, such fine abrasive particles are provided in a distribution of
particle sizes with a median particle diameter of about 60 microns or
less. In the preparation of hand pads to be used in the aforementioned
automotive applications, for example, the median particle diameter may be
smaller than 60 microns. In such articles, a median particle diameter of
40 microns or less is somewhat more preferred. Included among the various
types of abrasive materials useful in the present invention are particles
of aluminum oxide including ceramic aluminum oxide, heat-treated aluminum
oxide and white-fused aluminum oxide; as well as silicon carbide, alumina
zirconia, diamond, ceria, cubic boron nitride, garnet, and combinations of
the foregoing. Useful abrasive particles may also include softer, less
aggressive materials such as thermosetting or thermoplastic polymer
particles as well as crushed natural products such as nut shells, for
example.
Those skilled in the art will appreciate that the selection of particle
composition and particle size will depend on the contemplated end use of
the finished abrasive article, taking into account the nature of the
workpiece surface to be treated by the article and the abrasive effect
desired. Preferably, the fine abrasive particles for inclusion in the
articles of the invention comprise materials having a Moh's hardness of at
least about 5, although softer particles may be suitable in some
applications, and the invention is not to be construed as limited to
particles having any particular hardness value. Preferably, in the
manufacture of hand pads for use in the foregoing automotive applications,
the fine abrasive particles comprise aluminum oxide particles having the
foregoing distribution of particle sizes. The particles are added to at
least one of the first or second major surfaces of the nonwoven web to
provide a particle loading which is adequate for the contemplated end use
of the finished article. In the preparation of articles for the
aforementioned automotive application, for example, the fine abrasive
particles may be applied to the web to provide an add-on weight within the
range from about 63 to 168 g/m.sup.2 (about 15 to 40 grains/24 in.sup.2).
The size coat precursor may be the same as the above discussed make coat
precursor, or it may be different than the make coat precursor. The size
coat precursor can comprise any of the aforementioned resinous or
glutinous adhesives such as phenolic resins, urea-formaldehyde resins,
melamine resins, acrylate resins, urethane resins, epoxy resins, polyester
resins, aminoplast resins, and combinations and mixtures of the foregoing.
Preferably, the size coat precursor will comprise a resinous adhesive
similar or identical to the adhesive used in the make coat precursor. More
preferably, the size coat precursor will comprise either a thermosetting
resin or a radiation curable resin. Most preferably, the size coat
precursor will comprise a thermosetting phenolic resin, as described
above. The size coat precursor preferably is foamed prior to its
application to the make coat, again to reduce the wet add-on weight of the
resin so that the abrasive particles are not buried within the resin
coating and rendered unavailable for use in the initial applications of
the finished article. Preferably, the size coat precursor is foamed to a
blow ratio between about 5:1 and about 25:1, more preferably about 20:1.
The foamed or frothed size coat precursor is preferably applied to the
nonwoven web to provide an add-on weight which covers the abrasive
particles with a thin and substantially uniform coating without burying
the particles under the resin. Where the aforementioned foamed phenolic
resins are applied to a nonwoven web having the aforementioned fiber
weight, preferably, the dried add-on weight for the size coat is within
the range from about 33 g/m.sup.2 to about 105 g/m.sup.2. However, the
specific add-on weights will depend on several factors such as the nature
of the nonwoven web (e.g., fiber weights, fiber types and the like) as
well as the nature of the resin being used. The determination of
appropriate size coat add-on weights is well within the skill of those
practicing in the field.
The make coat precursor or the size coat precursor or both can contain
optional additives, such as fillers, fibers, lubricants, grinding aids,
wetting agents, surfactants, pigments, dyes, coupling agents,
plasticizers, suspending agents, antistatic agents and the like. Possible
fillers include calcium carbonate, calcium oxide, calcium metasilicate,
alumina trihydrate, cryolite, magnesia, kaolin, quartz, and glass. Fillers
than can function as grinding aids include cryolite, potassium
fluoroborate, feldspar, and sulfur. Fillers can be used in amounts up to
about 400 parts, preferably from about 30 to about 150 parts, per 100
parts of the make or size coat precursor, while retaining good flexibility
and toughness of the cured coat. The amounts of these materials are
selected to provide the properties desired, as known to those skilled in
the art.
Organic solvent and/or water may be added to the precursor compositions to
alter viscosity. Preferred viscosity values before foaming range between
10 to 10,000 cps (as measured using a Brookfield viscometer), usually
between 50 to 1,000 cps, at room temperature (e.g., 25.degree. C.). The
selection of the particular organic solvent and/or water is believed to be
within the skill of those practicing in the field and depends upon the
thermosetting resin utilized in the binder precursor and the amounts of
these resins utilized.
As seen in FIG. 3, in the preparation of the articles of the invention the
lofty nonwoven web 110 having first side 114 and second side 116 is fed
into apparatus 14. At this stage, the nonwoven web 110 is preferably a
pre-bonded web, not yet comprising abrasive particles. The nonwoven web
110 is first passed through coater 20 which applied first adhesive or make
coat precursor to the web 110. The coater 20 can comprise any suitable
coater known in the art, such as a spray coater, roll coater, dip coater,
knife over roll coater, or the like. When applying the preferred foamed
make coat precursor described below, the preferred coater 20 comprises a
double roll coater with the web 110 passing through the nip formed by the
two opposed rollers. Such coaters are well known in the art need not be
further described herein. The foamed make coat precursor is applied to the
top roller from a frother through a slot die as is known in the art. In
one preferred embodiment, the frother is of the type commercially
available as a "F2S-8" from SKG Industries, West Lawn, Pa. Other suitable
arrangements for applying the frothed make coat precursor to the web
include but are not limited to: applying the make coat precursor with a
slot die to the bottom roll or to both rolls of a double roll coater;
applying the make coat precursor with a slot die directly to the web prior
to entering the nip of a double roll coater; applying the make coat
precursor with a slot die without a roll coater and optionally by drawing
a vacuum across the web opposite the slot die, applying the make coat
precursor to both sides of the web with opposed slot dies with or without
subsequently passing the web through a roll coater; and applying the make
coat precursor with a hose or duct transversing across the web.
After exiting the first adhesive coater 20, web 110 passes through first
particle coater 22. First particle coater 22 is preferably configured to
apply abrasive particles 112 to the first surface 114 of the web. As
explained further below, the abrasive grains 112 will penetrate from
surface 114 to some depth into the web 110. When it is desired to apply
abrasive grains to second side 116 of the web 110, the web passes over
rollers 24a and 24b so as to re-orient the web to have second side 116
facing up. The web 110 then passes through an optional second particle
coater 26 configured to apply abrasive particles 112 to the second side
116 of web 110. Preferably, second particle coater 26 is of like
construction as first particle coater 22. However, for certain
applications, it may be preferable to use second coater 26 of a different
type or configuration from first particle coater 22. Also, the second
abrasive particle coater 26 may apply abrasive particles having either the
same or different composition and/or size as the abrasive particles
applied by the first abrasive particle coater 22.
After applying fine abrasive particles 112 to at least the first surface
114 of web 110, and optionally to second surface 116, the web 110 is
preferably exposed to a heat source (not illustrated), such as infrared
lamps or an oven, to heat the make coat precursor to the extent necessary
to at least partially cure the resin. In some applications, it may be
preferable to fully cure the make coat precursor at this step. Heating can
be done with any source giving sufficient heat distribution and air flow.
Examples of suitable heat sources include forced air oven, convection
oven, infrared heat and the like. It is also within the scope of the
invention to use radiation energy. For heat-activatable thermosetting
resin foams, it is preferred that heating be for a sufficient amount of
time to at least drive off solvent (e.g., water) and initiate at least
partial curing (cross-linking) of the resin.
In a preferred embodiment, the web 110 optionally passes through second
adhesive or size precursor coater 28 to apply an optional but preferred
size coat precursor to the web 110 after it exits the second abrasive
particle coater 26. Preferably, the size precursor coater is of the same
configuration as the make precursor coater 20. For some applications, it
may instead be desired to use a coater 28 of a different configuration
from that of the first coater 20. In some applications, it may be
preferred not to add the size coat.
A preferred embodiment of first particle coater 22 is illustrated in
greater detail in FIG. 4. Web 110 is conveyed through the coater 2 by a
carrier belt 30 which passes around rollers 32a and 32b, at least one of
which is a drive roller. The web 110 passes through particle spray booth
34. Booth 34 includes first side 36, second side 38, top 40, and bottom
42. Booth 40 also includes front and back sides not illustrated. First
side 36 includes entry slot 44a sized and configured to allow web 110 and
carrier belt 30 to enter the booth 34. Second side 38 includes exit slot
44b sized and configured to allow web 110 and belt 30 to exit the booth
34. Slots 44a, 44b are located near the bottom of sides 36, 38
respectively. Mounted through an opening in the top 40 of the booth 34 is
particle sprayer 46, having deflector 48 mounted at the exit 47 of the
sprayer. The web 110, which at this point includes a make coat precursor
thereon, is carried by belt 30 through the booth 34. As the web passes
from entry slot 44a to exit slot 44b, particle sprayer 46 introduces
particles 112 into the booth so as to coat the first side 114 of the web
with abrasive particles. As described below, the particles 112 will
penetrate to some depth into the web 110. The web 110, now comprising
abrasive particles adhered to the web by the make coat precursor, then
exists the booth 34.
In one preferred embodiment, the particle sprayer 46 receives an abrasive
particle/air mixture from fluidizing bed 52. Abrasive particles 112 are
fluidized in the bed 52 by fluidizing air (from a suitable source, not
illustrated), introduced into the bed via fluidizing air inlet 53. The
fluidizing air flow rate should be high enough to cause fluidization,
without being so high so as to cause "worm holes" through the bed, i.e., a
small number of discrete locations where the air passes through the
particles without causing significant fluidization throughout the bed. The
flow rate of fluidizing air should also be selected to minimize
"stratification" of the particles 112, i.e., a state in which smaller
particles tend to migrate toward the top of the bed while larger particles
tend to migrate toward the bottom of the bed.
Atop the fluidizing bed 52 is a venturi inlet 56 as is well known in the
art. In the illustrated embodiment, venturi 56 receives primary air from a
suitable source via primary air inlet 58. The primary air passes through
the venturi 56 drawing the mixture of fluidized particles and air through
the draw tube 54 which extends from the venturi 56 into the fluidizing bed
52. Secondary air optionally can be added to the venturi inlet 56 via
secondary air inlet 60. The secondary air is added to the flow of
fluidized abrasive particles after the particles are drawn into the
venturi to aid in delivering the fluidized abrasive particle/air mixture
to the sprayer 46 via particle hose 64 which extends from the venturi exit
62 to the inlet of the particle sprayer 46.
The deflector 48 mounted in the exit 47 of the particle sprayer 46
redirects the fluidized abrasive particle/air mixture. Deflector 48
includes deflector top 49 (illustrated in FIGS. 5 and 6), deflector bottom
50, and deflector wall 51. To obtain the preferred uniform distribution of
fine abrasive particles on web 110 described above, the present inventors
have discovered that it is preferable to redirect the flow of the
fluidized abrasive particle/air mixture so as not to spray the mixture
directly into the web 110. Instead, the desired uniform distribution of
abrasive particles 112 is achieved with the method and apparatus of the
present invention by creating a uniformly dispersed cloud of abrasive
particles in the spray booth 34 above the web 110 having the liquid make
coat precursor thereon. The cloud then deposits, preferably by settling
due to gravity onto the web 110 in the desired uniform patter. Such a
uniformly dispersed cloud helps prevent the individual fine abrasive
particles from agglomerating or clumping together. Instead, the abrasive
particles settle from the cloud onto the web having the make coat thereon
as illustrated in FIG. 4. In one preferred arrangement, the deflector
bottom 50 has a diameter of 32 mm (1.26 inches), the bottom edge of the
deflector extends 20 mm (0.79 inches) from the exit of the spray gun, and
is held at a height of 155 mm (6.1 inches) above the nonwoven web 110. Of
course, other arrangements fall within the scope of the present invention.
For example, the size of the deflector, the shape of the deflector, the
contour of wall 51, the number and location of particle sprayers 46, the
height of the deflectors above the web, the speed of the web 110, ad the
air pressure and ratio of abrasive particles in the particle/air mixture
can each be varied. Such parameters can be varied to achieve the desired
add-on weight of abrasive particles, the desired penetration into the web
110 of the abrasive particles, and the desired uniformity of the abrasive
particles 112 on the web 110.
In one preferred embodiment, sprayer 46, fluidizing bed 52, and controller
(not illustrated) is a commercially available system known as MPS 1-L
Manual Powder System, including model PG 1-E Manual Enamel Powder Gun,
available from Gema, an Illinois Tool Works Company, of Indianapolis,
Ind., with a round deflector 48 substantially as illustrated in FIG. 4.
In another preferred embodiment, the abrasive particle spray apparatus is
of the type commercially available from Binks Manufacturing Company
(Sames), of Franklin Park, Ill., and includes a 50 lb. Fluidized bed, a
GCM-200 Gun Control Module, a SCM-110 Safety control Module, a STAJET SRV
Type 414 gun, with a standard powder pump.
Another preferred embodiment of particle sprayer 46 is illustrated in FIGS.
5 and 6. In this embodiment, the sprayer comprises an elongate tube 66
having an exit 47 at one end and an inlet 68 at the opposite end of the
tube. In use, this embodiment of the sprayer 46 has the abrasive
particle/air mixture hose 64 attached to the inlet 68 as is illustrated
with respect to the earlier described embodiment of FIG. 4. The embodiment
of the sprayer 46 illustrated in FIGS. 5 and 6 is mounted in spray booth
34 and operates as described with respect to the embodiment of particle
coater 22 illustrated in FIG. 4.
Returning to FIGS. 5 and 6, sprayer 46 includes particle deflector 48
mounted at exit 47 of tube 66. Deflector 48 is mounted to the tube 66 by
any suitable mounting means. In one preferred embodiment, deflector mount
70 includes a base 72 comprising a generally rectangular plate having a
first end 74 and a second end 76. Base 72 is sized and configured to fit
in slot 69 in the end of tube 66 proximate the exit 47. Mount 70 can be
permanently or removably mounted to the tube 66. In the illustrated
embodiment, base 72 is releasably held in slots 69 by a spring, clip, or
other suitable fastener (not illustrated) affixed to holes 78 in the first
and second ends of base 72. Extending from base 72 is a threaded rod 80
having a first end 82 affixed to the base (such as by brazing, for
example) and second end 84 extending beyond the exit 47 of tube 66.
Threaded rod 82 is configured to engage with a like-threaded hole in the
top 49 of deflector 48. This allows the position of deflector 48 to be
conveniently adjusted with respect to the exit 47 of the tube 66 by
rotating the deflector 48. This allows for varying the direction of motion
of the particles 112 leaving the sprayer 46 as described above. Deflector
48 also includes bottom 50 opposite top 49, and deflector wall 51
extending between top 49 and bottom 50.
An alternate embodiment of sprayer 46 is illustrated in FIG. 6A. In this
embodiment, threaded rod 80 is elongated, and includes a tapered end 82 to
help direct the flow of abrasive particles through tube 66. Pins 73 extend
through holes 75 in the wall of the tube 66, and extend through holes in
the rod 80, to mount the rod 80 in the sprayer 46. In one embodiment, the
tapered end 82 of rod 80 ends at the inlet 68. In other embodiments, the
end 82 can extend beyond the inlet 68, or the inlet may extend beyond the
end 82 of the rod. Deflector 48 is mounted on threaded end 84 as described
above.
The tube 66 and deflector 48 should be sized and configured to provide the
desired uniform spray pattern of abrasive particles 112. In one preferred
embodiment, tube 66 is approximately 61 cm (24 inches) long, has an inside
diameter of 1.08 cm (0.425 inches), and an outside diameter of 1.27 cm
(0.5 inches), and is constructed of stainless steel. It is understood that
other sizes and materials of tube 66 fall within the scope of the present
invention.
Another preferred embodiment of the abrasive particle sprayer 46 is
illustrated in FIG. 7. In this embodiment, the sprayer 46 comprises
rotating first and second circular discs 90 and 91, respectively, joined
by studs 93. Second disc 91 has a hole 92 in the center thereof. Second
disc is joined to rotating shaft 94 which is concentric with the center
hole 92. Rotating shaft 94 is rotatably mounted on the outside of
stationary feed tube 95 by means of bearings 98, such that rotating shaft
94 is concentric with stationary feed tube 95. In this manner, rotating
shaft 94, first plate 90, and second plate 91 are able to rotate together
as a unit about stationary feed tube 95. The rotating shaft 94 can be
driven by any suitable power means, such as an air motor (not
illustrated). Feed tube 95 includes inlet 96 and outlet 97. In one
preferred embodiment, inlet 96 of the feed tube 95 is attached to abrasive
particle/air mixture hose 64, and the particle sprayer 46 is mounted on
the top 40 of particle booth 34 as explained with regard to the embodiment
of FIG. 4. In such an arrangement, the particle sprayer 46 receives
fluidized abrasive particles from the fluidizing bed 52. In a variation of
this embodiment, a vibratory feeder can be used in place of the fluidizing
bed 52. The vibratory feeder is connected to feed abrasive particles into
the inlet 96 of feed tube 95.
In operation, the rotating shaft 94 is driven so as to cause plates 90 and
91 to rotate. Abrasive particles pass through feed tube 95 and exit from
outlet 97. Tube outlet 97 is positioned through hole 92 in second plate 91
such that the abrasive particles enter the space between first and second
plates 90, 91. The abrasive particles strike the top surface of rotating
plate 90, and will be dispersed through exit 47 in a direction generally
parallel to the plane of first and second plates 90, 91. The particles
preferably form a cloud that deposits, preferably by settling due to
gravity onto the surface of web 110 as explained with regard to the
embodiments described above. In one preferred embodiment, particle sprayer
46 comprises a Binks EPB-2000, commercially available from Binks
Manufacturing Company (Sames), of Franklin Park, Ill., and the abrasive
particles are fed to the particle sprayer by a vibratory pre-feeder
commercial available as "Type 151" from Cleveland Vibratory Company,
Cleveland, Ohio. The plates 90, 91 of the particle sprayer are preferably
driven at 6,000 to 9000 RPM, however slower and faster speeds are within
the scope of the present invention. The abrasive particle feed rate, type
of particle feeder, and rotational speed of the plates can be selected to
provide the desired abrasive particle spray pattern, desired abrasive
particle add-on weight, and desired degree of penetration into web 110 of
the abrasive particles.
What is common to the preferred embodiments described herein is that the
particle sprayer includes means to change the direction of flow of
particles 112 exiting the sprayer from perpendicular to the web 110, to a
direction approaching, or exceeding, a plane parallel to web 110. Such
directions are described with reference to the area immediately surround
the exit 47 of particle sprayer 46. Thereafter, the particles 112
preferably disperse into a cloud of particles in the booth 34. The
particles then settle from the cloud onto the web under the influences of
gravity. Thus in one preferred embodiment of the inventive method,
immediately before the particles adhere to web 110, gravity has a greater
effect on the motion of the abrasive particles than does the momentum
imparted by the particle sprayer 46. In some applications, the momentum
imparted by the particle sprayer 46 will have little or no effect on the
motion of the particles 112 immediately before the particles adhere to web
110. In other applications, for example where greater penetration of
abrasive particles 112 into the web 110 is desired, the above apparatus
parameters and configuration may be selected such that the downward
momentum imparted to the particles 112 by the sprayer 46 will have a
greater effect on the motion of the particles immediately before the
particles adhere to the web.
In the embodiments described with respect to FIGS. 3, 5, and 6, the means
for directing the flow of particles 112 exiting the particle sprayer 46 is
the deflector wall 51 of deflector 48. Preferably, the location of the
deflector 48 relative to the exit 47 of the particle sprayer can be varied
to obtain the desired redirection of flow of abrasive particles 112
exiting the particle sprayer. It will be appreciated that without the
deflector 48, the abrasive particles exiting the particle sprayer 46 will
travel generally parallel to the longitudinal axis of the sprayer, which
is generally perpendicular to the web 110. Generally, the closer the wall
51 and bottom 50 of the deflector are to the exit 47, the greater change
in direction of motion of particles 112 from perpendicular to the web 110
will be. Moving the wall 51 and bottom 50 of the deflector further from
the exit 47 will reduce the amount the direction of motion of the
particles is varied from perpendicular to the web 110. In the embodiment
described with respect to FIG. 7, the means for directing the flow of
abrasive particles is the rotating plates 90, 91.
In some applications, it may be desirable to place hard insects, such as
ceramic inserts, into those components of the apparatus 14 that are prone
to wear under prolonged flow of abrasive particles through the components.
This may be desirable, for example, in the particle sprayer 46, the
venturi inlet 56, and the deflector 48. Such interest would prolong the
useful life of certain components of apparatus 14, but would not be
expected to have a significant effect on the performance of the apparatus.
For some applications, it is preferable to use a plurality of particle
sprayers 46 in a single spray booth 34. Preferably, each of the particle
sprayers are of like configuration, however it is understood that
different types of particle sprayers could be used in a single booth. The
particle sprayers 46 should be arranged in a pattern that provides a
uniform coating of abrasive particles 112 to the web 110 as the web passes
through the booth 34. This can be accomplished by arranging the plurality
of particle sprayers 46 such that teach location across the width of the
web 110 from first edge 117 to second edge 118 traverses through an equal
number of spray patterns 45 caused by each of the particle sprayers 46.
Exemplary particle sprayer arrangements are illustrated schematically in
FIGS. 8A through 8D. These figures are schematic top views of the web 110
passing under the spray patterns 45 created by particle sprayers 46
mounted in the top 40 of the booth 34 (not shown). It is possible to vary
the flow rates of each of the plurality of sprayers 46, or to use
different configurations of sprayers 46 to obtain a desired coating
pattern of abrasive particles 112 on web 110. It is also possible to
oscillate or reciprocate the particle sprayers 46 to achieve a desired
spray pattern as is known in the art.
When using a plurality of particle sprayers 46, it is possible to use a
like number of particle coaters 22 as illustrated in FIG. 4, where each
particle sprayer receives abrasive particles 112 for a respective
fluidizing bed 52. In some applications it is preferable to feed a
plurality of particle sprayers 46 from a single fluidizing bed 50. In one
such arrangement, a plurality of venturi injectors 56 are mounted on a
single fluidizing bed. In an alternate arrangement, a plurality of
volumetric control auger feeders are mounted on the side wall of a
fluidizing bed to draw a desired rate of fluidized abrasive particle/air
mixture from the fluidizing bed 50. The operation and design of such
feeders is well known and need not be further discussed. Each auger feeder
deposits the abrasive particles into a venturi injector 56 as described
above. Each venturi injector 56 is connected to an abrasive particle/air
mixture hose 64 for conveying the abrasive particle/air mixture to a
particle sprayer 46 as described above. In one preferred embodiment, the
fluidizing bed 50 having a plurality of auger feeders mounted thereon is
of the type commercially available as the "Powder Delivery Control Unit"
Gema, and Illinois Tool Works Company, of Indianapolis, Ind. It is also
within the scope of the invention for the auger feeder to feed abrasive
particles from a volumetric feeder of the type commercially available as
"Dry Material Feeder" from AccuRate of Whitewater, Wis.
It is also within the scope of the present invention to include additional
particle sprayers configured to spray abrasive particles onto the web 110
with enough force to achieve greater penetration into the center portion
of the web. Such additional particle sprayers can be included in the spray
booth 34 along with the particle sprayers 46 described above, either in
the arrangement of particle sprayers 46, or arranged to spray the web 110
before or after the web passes under sprayers 46. Such additional sprayers
could also be arranged in a second particle spray booth before or after
the sprayers 22, 26, described above. Preferably, the additional sprayers
are arranged to deposit abrasive particles onto the web before the
sprayers 46, so as not to disturb or disrupt the advantageous spray
pattern achieved by the sprayers 46. Such a combination of sprayers can be
used to provide a web 110 having the advantageous fine particle
distribution at surfaces 114, 116 as described herein, along with
particles in the center portion of the web for a longer-life abrasive
article.
In one preferred embodiment, the web 110 has a width from first edge 117 to
second edge 118 of 61 cm (24 inches) and is fed through apparatus 14 at a
web speed of from about 3 to 30 meters/minute (10 to 100 feet/minute),
more preferably 16 meters/minute (52.5 feet/minute). The first adhesive
coater 20 is a double roll coater with the web 110 passing through the nip
formed by the two opposed rollers. The foamed make coat precursor is
applied to the top roller from a frother through a slot die as is known in
the art. In one preferred embodiment, the frother is of the type
commercially available as a "F2S-8" from SKG Industries, West Lawn, Pa.
The abrasive particles 112 are applied by eight particle sprayers 46
generally as described with respect to FIGS. 5 and 6, fed by eight venturi
injectors 56 mounted on a fluidizing bed 52. The spray pattern of the
injectors is generally as illustrated with respect to FIG. 8B. The
abrasive particles 112 preferably comprise aluminum oxide particles having
a median particle size of about 60 microns, applied to each side in an
amount of from about 63 to 168 grams/m.sup.2 (about 15 to 40 grains per 24
square inch), more preferably in an amount of about 105 grams/m.sup.2 per
side (25 grains per 24 square inch). The make coat precursor is then
partially cured. The second adhesive coater 26 preferably is of the same
type as the first adhesive coater 20. The size coat precursor preferably
has the same composition as the make coat precursor, is frothed to a
desired blow ratio, and is applied in an amount to provide a suitable dry
add-on weight as mentioned above. The parameters for the Gema particle
coater described above are as follows: fluidizing air introduced through
inlet 53 at a pressure of from about 2 to 15 psi; primary air introduced
into inlet 58 of venturi 56 at a pressure of up to 90 psi, preferably 30
to 60 psi; secondary air introduced into inlet 60 at a pressure of from 0
to about 90 psi, preferably from 0 to about 20 psi.
The methods and apparatuses described herein provide the advantageous
abrasive article as illustrated in FIG. 2. By applying the foamed make
coat precursor in the manner described herein, the tendency for the make
coat precursor to migrate to concentrate and agglomerate is reduced. In
this manner, the fibers 100 of the web are uniformly coated with the make
coat precursor, allowing the abrasive particles 102 to be coated onto and
adhered to the fibers in a more uniform distribution. And by coating the
make coat precursor and abrasive particles in different steps, the
abrasive particles are less likely to be "buried" within the make coat as
is prone to happen in the prior art method of applying a make coat
precursor/abrasive particle slurry. In the finished articles made by the
method and apparatuses of the invention, the size coat provides a light
coating of resin over the fine abrasive particles without burying the
particles within the resin. When observed under a microscope, for example,
the individual particles are observed to be anchored to the fibers and to
extend outwardly from the outer surfaces of the fibers. In this
construction, the fine abrasive particles are positioned in the article to
be immediately abrasively effective in the initial applications of the
finished article. Moreover, the particles are strongly adhered to the
fibers of the web to provide an abrasive article with a satisfactory work
like.
TEST METHODS
In the Examples set forth below, the following test methods were employed.
Scuffing Test
A scuffing test was used to simulate the abrasive qualities of abrasive
articles on typical painted automotive surfaces. The test specimens are
prepared from poly(methyl) methacrylate sheet material 1/8 inch (3.2 mm)
thick. Rockwell Ball Hardness of 90-105, available in 48.times.96-inch
(1.22.times.2.44 m) sheets under the trade name "Acrylite" from American
Cyanamid, Wayne, N.J. Following the removal of the protective covering
from the top side of the acrylic sheet, a double coat of "PPG Black
Universal Base Coat" paint (PPG Industries Inc., Automotive Finished
Division, Cleveland, Ohio) was applied per the manufacturer's
recommendations. The black base coat was painted over with three (3)
double coats of "PPG Paint DAU 82, Clear" (PPG Industries, Inc.,
Automotive Finishes Division, Cleveland, Ohio) per the manufacturer's
recommendations, allowing about 30 minutes of "flash time" between each
double coat application. The coated sheets were allowed to air-dry for
approximately 72 hours. 4-inch (10.2 cm) diameter test specimens were cut
from the coated sheet with care taken to minimize the scratching of the
painted surface. The cut discs were then baked at 150.degree. F.
(66.degree. C.) in an oven, avoiding any contact with the coated surface,
for about 16 hours to fully cure the paint coatings. The test specimens
were then ready for testing.
The tests were conducted on a Schiefer Abrasion Machine (available from
Frazier Precision Company, Gaithersburg, Md.) fitted with a spring clip
retaining plate to secure the painted test specimen on the bottom
turntable and a mechanical fastener ("3M Scotchmate Dual Lock" SJ3442 Type
170) to hold the abrasive composition on the upper turntable. For each
test, the counter was set to run 500 revolutions. A 4-inch (10.2 cm)
diameter disc of the abrasive article to be tested was cut and mounted on
the upper turntable via the mechanical fastener. In the event that the
abrasive article had contact surfaces significantly different from each
other, notation was made as to which side was being tested. A
previously-prepared 4-inch (10.2 cm) diameter painted acrylic disc was
weighted to the nearest milligram (W.sub.1) and mounted via the spring
clip to the lower turntable with the painted surface facing up. A 10 lb.
(4.55 kg) weight was placed on the load platform of the abrasion tester.
If the abrasion tester is plumbed for wet testing, the water supply is
shut off. The upper turntable was lowered to contact the painted acrylic
disc under the full force of the load weight, and the machine was started.
After 500 revolutions, the machine was turned off, the abrasive article
removed from the upper turntable and discarded, and the painted acrylic
disc was removed from the lower turntable. Any free dust or detritus was
removed from the painted acrylic disc by wiping with a dry paper towel and
the disc weighed gain (W.sub.2). The difference W.sub.1 -W.sub.2 is
reported to the nearest milligram as "cut".
The test should not abrade the painted acrylic disc to the extent that any
of the underlying black paint is removed. In the event that the abrasion
progressed through the black layer, the test was repeated. In the event
that the abrasion passes through the black layer on the second attempt,
new painted acrylic discs should be prepared with additional layers of the
clear coating.
MATERIALS DESCRIPTION
In the Examples that follow, the materials are referred to as follows:
Nylon Staple Fiber: is 12 denier (13.3 dtex).times.38 mm nylon 6,6 staple
fibers, commercially available under the trade designation "T-885" from
DuPont Canada Inc., Mississauga, Ontario, Canada.
Phenolic Resin: is a resole precondensate commercial available under the
trade designation "BB077" from Neste Resins Canada, a Division Of Neste
Canada Inc., Mississauga, Ontario, Canada.
Antifoam: is a silicone antifoam compound commercially available under the
trade designation "Q2" from Dow Corning Corp., Midland, Mich.
Surfactant: is a surfactant commercial available under the trade
designation "Sulfochem SLS", from Chemron Corporation, Paso Robles, Calif.
Red Dye Premix: is a mixture consisting of 14 parts red pigment (Ciba-Geigy
Corp., Pigments Division, Newport, Del.), two parts "Black Dye Nigro
Eclacid" (Rite Industries, Inc., High Point, N.C.), and 84 parts water.
Abrasive Particles: is ANSI grade 280 and finer Al.sub.2 O.sub.3 particles
having a median particle diameter of about 28 microns
EXAMPLES
The following non-limiting examples further illustrate the utility,
performance and comparative advantages of the articles of the invention.
Unless otherwise indicated, all parts and percentages are by weight.
Example 1
A lofty, random air-laid fabric was formed on a "Rando Webber" machine
(Rando Machine Corporation, Macedon, N.Y.) consisting of 147 g/m.sup.2 of
12 denier.times.38 mm Nylon Staple Fibers. The web was approximately 61 cm
wide. A prebond coating having the composition set forth in Table 1 was
applied to the air-laid fabric to achieve a dry add-on weight of 109
g/m.sup.2. The prebond was then cured in an oven at 170.degree. C. for 105
seconds. A make coat precursor having the composition set forth in Table 1
was frothed using a frother (commercially available under the trade
designation "F2S-8" from SKG Industries, West Lawn, Pa.) as per the
manufacturer's recommended procedure with a blow ratio of about 17:1. The
frothed make coating was delivered to the top roll of a two-roll coater
via a slot die, whereby the frothed make coat precursor was applied to the
previously-coated and cured prebonded web to provide a make coat dry
add-on weight of 63 g/m.sup.2. Abrasive Particles were applied to the
uncured make coat precursor at an add-on weight of 105 g/m.sup.2 to each
side of the froth-coated web via a particle sprayer (commercially
available under the trade designation "Sames EPB 2000", Binks
Manufacturing company, Franklin Park, Ill.) operated at approximately
9,000 RPM. The Abrasive Particles were drop fed into the particle sprayer
without feed air from a vibratory pre-feeder (commercially available under
the trade designation "Type 151", Cleveland Vibratory Company, Cleveland,
Ohio). The exit of the particle sprayer was adjusted to a sufficient
height above the surface of the web to deposit particles across the entire
surface of the web. The web was passed underneath the sprayer at a web
speed of approximately 7.6 meters/minute (25 feet/minute). The
abrasive-coated web was then cured in an oven at 148.degree. C. for 72
seconds followed by further heating at 160.degree. C. for 72 seconds. A
size coat precursor of the composition shown in Table 1 was frothed at a
blow ratio of about 17:1 and applied in the same manner as the make coat
precursor to provide a dry size coat add-on weight of 92 g/m.sup.2, and
the size coat precursor was subjected to a final cure in an oven at
148.degree. C. for 72 seconds followed by heating at 160.degree. C. for 72
seconds. Test specimens were evaluated according to the Scuffing Test
procedure. The results are summarized in Table 2.
Example 2
Example 2 was made according to the procedure and materials used in Example
1 with the following exceptions: 1) the compositions used as the prebond,
make coat and size coat precursors are set forth as "Example 2" in Table
1; 2) the make coat precursor dry add-on weight was 50 g/m.sup.2 ; 3) the
size coat precursor dry add-on weight was 63 g/m.sup.2 ; 4) Abrasive
Particles were applied to only one side of the web with an add on weight
of 105 g/m.sup.2, applied by four particle sprayers of the type
illustrated in FIG. 6A which were positioned generally as illustrated with
respect to FIG. 8D at a height of 155 mm above the surface of the web. The
particle sprayers were fed by four venturi injectors 56 mounted on a
fluidizing bed 52 as described with respect to the embodiment illustrated
in FIG. 3. The parameters for the particle coater were as follows:
fluidizing air introduced through inlet 53 at a pressure of about 5 psi;
primary air introduced into inlet 58 of venturi 56 at a pressure of about
60 psi; no secondary air was used, the 61 cm (24 inches) wide web was fed
at a web speed of 15.4 meters/minute (50 feet/minute); 5) the make coat
precursor was cured at only the 148.degree. C. temperature for 72 seconds;
and 6) the size coat precursor composition was cured at 148.degree. C. for
432 seconds. Test specimens were tested according to the Scuffing Test,
and the results are summarized in Table 2.
Comparative Example A
Comparative Example A is a commercially-available nonwoven abrasive surface
conditioning material having the trade designation "SCOTCH-BRITE 07447
A-VFN General Purpose Hand Pad" available from the Minnesota Mining and
Manufacturing Company of St. Paul, Minn. The pad comprises a nonwoven
substrate having a fiber weight of about 147 g/m.sup.2, a total resin
weight of about 250 g/m.sup.2 and a mineral loading of about 210
g/m.sup.2. The mineral used in this pad is aluminum oxide of grade 280 and
finer having a median particle diameter of about 28 microns. Comparative
Example A was tested according to the Scuffing Test procedure, and the
results are summarized in Table 2.
TABLE 1
______________________________________
Coating Compositions
Coating Component Example 1 Example 2
______________________________________
Preband Phenolic Resin
73.2 parts 73.2 parts
water 20 parts 20
parts
Red Dye Mix 6 parts 6 parts
Antifoam 0.015 parts 0.015
parts
Make Phenolic Resin 62 parts 60
parts
water 31 parts 33
parts
Surfactant 3 parts 3 parts
Red Dye Mix 4 parts 3 parts
Size Phenolic Resin 62 parts 60
parts
water 31 parts 33
parts
Surfactant 3 parts 3 parts
Red Dye Mix 4 parts 3
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parts
TABLE 2
______________________________________
Scuffing Test
Initial weight,
Final weight,
Cut, grams
Average Cut,
Example grams grams removed grams
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1 27.186 26.889 0.297
1 27.048 26.730 0.318 0.308
2 27.333
27.034 0.299
2 27.449 27.124 0.325
2 27.598 27.297 0.301 0.038
Comp. A 25.807
25.724 0.083
Comp. A 27.088 26.999 0.089
Comp. A 25.807 25.724 0.083
Comp. A 27.088 26.999 0.089
0.086
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The results of the comparative testing in Table 2 indicate that the amount
of cut for the articles of the invention are unexpectedly high and greatly
in excess of the cut provided by the article of Comparative Example A. The
article of Comparative Example A provided an average cut that was only 28%
of the cut provided by the inventive pad of Example 2 and 28% of the cut
provided by the inventive pad of Example 1.
The present invention can be used to abrade and/or polish a wide range of
workpiece surfaces. These workpiece surfaces include metal (including mild
steel, carbon steel, stainless steel, gray cast iron, titanium, aluminum
and the like), metal alloys (copper, brass and the like), exotic metal
alloys, ceramics, glass, wood (including pine, oak, maple elm, walnut,
hickory, mahogany, cherry and the like), wood like materials (including
particle board, plywood, veneers and the like) composites, painted
surface, plastics (including thermoplastics and reinforced
thermoplastics), stones (including jewelry, marble, granite, and semi
precious stones), glass surfaces including glass television screens,
windows (including home windows, office windows, car windows, air windows,
train windows, bus windows and the like); glass display shelves mirrors
and the like) and the like. The abrasive article may also be used to clean
surfaces such as household items (including dishes, pots, pans and the
like), furniture, walls, sinks, bathtubs, showers, floors and the like.
The workpiece may be flat or may have a shape or contour associated with
it. Examples of specific workpieces include ophthalmic lenses, glass
television screens, metal engine components (including cam shafts,
crankshafts, engine blocks and the like), hand tools, metal forgings,
fiber optic polishing, caskets, furniture, wood cabinets, turbine blades,
painted automotive components, bath tubs, showers, sinks, and the like.
Depending upon the particular application, the force at the abrading
interface can range from about 0.01 kg to over 100 kg, typically between
0.1 to 10 kg. Also depending upon the application, there may be a
polishing liquid present at the interface between the abrasive article and
the workpiece. This liquid can be water and/or an organic solvent. The
polishing liquid may further comprise additives such as lubricants, oils,
emulsified organic compounds, cutting fluids, soaps and the like. The
abrasive article may oscillate at the polishing interface during use.
The abrasive article of the invention can be used by hand or used in
combination with a machine. For example, the abrasive article may be
secured to a random orbital tool or a rotary tool. At least one or both of
the abrasive article and the workpiece is moved relative to the other.
The details of the preferred embodiment have been described in detail to
provide an understanding and an appreciation of the invention. Of course,
minor changes and modifications can be made to the preferred embodiment by
those skilled in the art without departing from the spirit and the scope
of the invention, as defined in the following claims.
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